In the United States v. Shreveport Grain & Elevator Co., 1932, the Supreme Court ruled on a case involving grain storage rates charged by an elevator company in Louisiana. The U.S. government argued that these rates were unreasonable and discriminatory, violating the Interstate Commerce Act which regulates economic activity across state lines to ensure fair competition. The Shreveport Grain & Elevator Company contended that its operations were purely intrastate (within one state) and thus not subject to federal regulation under this act. However, the court disagreed with their argument stating that even though their activities might be local in character if they have a substantial effect on interstate commerce then they can be regulated by Congress under its commerce power as per Constitution's Commerce Clause. The decision upheld federal authority over intrastate commercial activities when those activities significantly impact interstate commerce - reinforcing principles established earlier in cases like Swift & Co v United States (1905). This ruling further expanded federal regulatory powers over business practices within individual states when such practices affect national trade or economy.

In the dissenting opinion for United States v. Shreveport Grain & Elevator Co., Justice McReynolds disagreed with the majority's interpretation of the Sherman Act and its application to this case. He argued that there was no evidence of a conspiracy to restrain trade or monopolize commerce, as required by law for conviction under the Act. Instead, he believed that any restraint on trade was incidental and not intentional - an important distinction in antitrust cases at that time. Furthermore, he contended that even if such a conspiracy existed, it would be within state lines and therefore outside federal jurisdiction according to his understanding of interstate commerce regulation at the time. Thus, Justice McReynolds concluded that both charges against Shreveport Grain & Elevator Co should have been dismissed due to lack of sufficient evidence proving intent or effect on interstate commerce.